1. Field of the Invention
The present invention relates generally to printing presses and more particularly to a device and method for driving a printing cylinder in a printing press.
2. Background Information
Printing cylinders of printing presses print a material, such as paper. In offset web printing, the printing cylinders include a plate cylinder and a blanket cylinder. Typically, a plate on the plate cylinder engages the blanket on the blanket cylinder, as a web or sheet of material passes between the blanket and an impression cylinder. Ink is transferred from an ink roller to the plate cylinder, and ink corresponding to an image is transferred to the blanket and then to the web or sheet. For two sided printing, the impression cylinder is another blanket cylinder.
The plate and blanket cylinders are driven on a gear side of a printing press by a drive mechanism, which typically comprises gearing for driving each of the printing cylinders. A single or multiple motors can power the drive mechanism. Hitachi-Seiko, for example, has a two motor drive for driving two printing cylinders in a four-cylinder printing unit. Heidelberg Web Press, Inc. has a three motor drive for driving three printing cylinders of a four cylinder printing unit.
In order to prevent wrap-up during a web break in web printing presses, or to change plates or blankets on the respective cylinders, it is sometimes necessary to throw-off the plate cylinder from the blanket cylinder, and also to throw-off the blanket cylinder from the impression cylinder. The mechanisms which move the printing cylinders are called throw-off mechanisms.
Because the plate and blanket cylinders still need to rotate during throw off, the drive mechanism must remain engaged during throw-off.
U.S. Pat. No. 5,678,485 purports to disclose an offset printing press having a counterpoise and lift mechanism. The counterpoise is provided for permitting an axial blanket or printing sleeve to be slid over a respective cylinder. The lift mechanism is a throw-off mechanism for throwing-off, for example, the plate cylinder. A drive mechanism is not disclosed.
U.S. Pat. No. 3,724,368 purports to disclose a drive mechanism and a throw-off mechanism for an offset printing press. An harmonic drive means provides for register adjustment of both plate cylinders. The primary drive for the printing press is provided through a motor connected to one of the blanket cylinders.
The printing press manufacturer MAN Roland has a direct drive for a blanket cylinder. The motor is moved during throw-off and the motor drives the blanket cylinder in a 1:1 ratio.
One problem with the above-devices is that the motors to drive the cylinders are large and space-consuming, and are often difficult to adjust. Moreover, the motors often must be moved along with the cylinders during throw-off, which can create a complicated and difficult structure.